According to the original concept of Power-over-Ethernet (PoE, see, for example, IEEE 802.3 af/at standard), every PoE device or powered device (PD) (e.g. luminaires, sensors etc.) has its own connection to the power sourcing equipment (PSE), because the power is distributed in a star like cabling structure, potentially increasing the total cable length.
In many installations cabling loads in a chain would be interesting, such that a part of the cable is shared by several loads. The individual nodes in a chain may even leverage from information on the number of loads in this PSE segment, e.g. in order to prevent overloading the PSE.
Upcoming solutions with a low voltage DC distribution e.g. following the PoE standard are hampered as infrastructure changes need to be done before new lighting devices can be mounted. Other DC distribution systems as used in lighting not adhering a PoE standard commonly have the same high investment in infrastructural change and small installations do mostly not make any commercial sense.
A typical PoE lighting system is illustrated in FIG. 1 with a PSE 1 and a number of PDs 2 in the form of luminaires. Each luminaire 2 is connected by a dedicated cable 3 to the PSE 1, which is provided with a mains connection 4 and an Ethernet connection 5. A typical luminaire 2 for such system comprises LED modules generating light and an electronic section controlling the LED current as well as interfacing to the PoE connection for negotiation and voltage adaptation.
US 2010/0217447 A1 is related to a detection of multiple powered devices connected to an inline power delivery channel. It is disclosed to provide multiple PDs (number n) such they each provide a resistance of n·25 kΩ, so that the parallel combination equals the standard 25 kΩ and is correctly detectable by the PSE. US 2010/0217447 A1, however, does not disclose how the number of PDs is determined in the first place and how the resistance provided by the PD (i.e. the multiple of 25 kΩ) is set.
US 2011/0885584 A1 is related to a long-reach Ethernet system and relay. A case is discussed where a number of relays and an Ethernet terminal are connected in parallel to form a powered load. In order to decrease an influence of the relays on the PD in-position detection, the in-position indication resistance of the relays is made much larger than 26.5 kΩ (>265 kΩ, e.g. 470 kΩ), such that the parallel in-position indication equivalent resistances of the relays and the PD are basically the same as the PD in the first place. It may be said that, according to US 2011/0885584 A1, the relays are made “invisible” in the parallel connection for detection by the PSE. However, due to the change in the in-position indication, the relays may not be connected to the PSE alone (or would at least not be detected as potential PDs).